EYE ON THE SKY
In the life of a galaxy, collisions don’t always mean destruction; they can often result in the chaotic birth of something new and beautiful
HUBBLE SPACE TELESCOPE, 28 SEPTEMBER 2017
This active, glowing object is NGC 4490, a galaxy that is still recovering from a collision with a smaller galactic neighbour. It was once a barred spiral, probably similar to the Milky Way, but its shape has been deformed due to its encounter with irregular galaxy NGC 4485, not seen here.
In this Hubble image, the most intense, destructive period of the collision is already over; the two galaxies have passed through each other and are speeding apart once more. NGC 4490, having lost its former spiral shape, is nicknamed the Cocoon Galaxy.
Such collisions don’t simply result in destruction and distortion, however. The sheer force and energy created in the galactic crash is enough to generate bursts of star formation out of the interstellar dust and gas, seen here as glowing pockets of red. This red is caused by dense clouds of ionised hydrogen being illuminated by the light of hot, newborn stars. NGC 4490 is classified as a starburst galaxy, which means that stars are forming at a rate quicker than the stellar ingredients can be replenished.
A thin bridge of stars, not seen in this image, connects the two galaxies as they speed away from one another. This bridge stretches for more than 24,000 lightyears.
Perhaps our own Galaxy will go through a similar event one day. It is thought that our neighbouring Andromeda Galaxy will collide with the Milky Way in about four billion years, with a potentially similar fallout to what astronomers have observed here.